Three Part Question

In a [patient with suspected pulmonary embolus] does the [does a negative IL D-dimer test] adequately [rule out the diagnosis]?

Clinical Scenario

A 30 year old woman presents to the emergency department with distressing, left sided pleuritic chest pain. She may have had a pulmonary embolism and you request a D-dimer. You know the lab in your hospital utilises the IL D-dimer test and wonder whether a normal result would be sufficiently sensitive to rule out a pulmonary embolus.

Search Outcome

6 papers were found from the above search. 4 were relevant. One further paper was found from hand searching journals and references. These 5 papers are shown in the table below.

Relevant Paper(s)

Author, date and country

Patient group

Study type (level of evidence)

Outcomes

Key results

Study Weaknesses

Legani C et al,1999,Italy

105 consecutive outpatients ?DVT

Prospective cohort

ROC curve to define max sensitivity of IL test

230ng/ml cut off sensitivity 100% specificity 77.2%

Patients ?DVT not PE
High prevalence DVT
Would not reflect an average emergency department population

van der Graaf F,2000

99 ?DVT outpatients
Comparison of 13 different D-dimer tests

Prospective cohort

IL test sensitivity

90%

Patients ?DVT not PE
High prevalence of DVT

IL test specificity

78%

Villa P et al,2000,Spain

86 patients with a moderate or high clinical suspicion DVT

Prospective cohort

Iltest using 255ng/ml cut off sensitivity

98.4%

Patients suspected of having DVT not PE
Cohort had high prevalence DVT
Venography not used

Iltest using 255ng/ml cut off specificity

33.3%

Iltest using292ng/ml cut off sensitivity

95.2%

Iltest using292ng/ml cut off

41.7%

Gold EIA elisa test sensitivity

90%

Gold EIA elisa test specificity

57.1%

Harper P et al,2001,New Zealand

235 patients presenting to emergency department with ?DVT

Prospective cohort

IL test (250 ng/ml cut off) Sensitivity

94.1%

All patients presented as ?DVT not PE
The gold standard venogram not used in diagnosis DVT
All patients underwent ultrasound (USS), but not all underwent more than one. Probable under-estimation of DVT prevalence
Patients were simply advised to return to the department if symptoms did not settle

Results combined for ?DVT and ?PE patients
Cut off level of 200ng/ml was used for IL test (much lower than most labs)

IL-test sensitivity

91%

Acculot sensitivity

91%

Simpli RED specificity

79%

IL-test specificity

74%

Acculot specificity

76%

Comment(s)

To date there have been few studies measuring the accuracy of this D-dimer test. Of note, there is almost no research looking in particular at patients presenting with symptoms of PE. The sensitivity of the IL test for ruling out DVT appears to lie somewhere between 90 and 100%. It is worth noting that all of these studies used a relatively low cut off level and it is worth being aware what the cut off level is in your hospital laboratory.

Clinical Bottom Line

The IL D-dimer test alone is not sufficiently sensitive to rule out pulmonary embolus. It must be used in conjunction with another test.